The overall goal of this program is to train fellows in areas of basic research relevant to Pediatric Infectious Diseases, especially those in the immunocompromised host. The fellowship is designed as an intensive laboratory-based research training program with 2 years of protected laboratory time and 1 year of clinical training. Research can focus on issues related to the pathogen or the host. Faculty with successful basic research programs will serve as laboratory mentors. These faculty, selected from the Departments of Pediatrics, Medicine, Biochemistry, and Microbiology and Immunology, have a documented history of productive collaborative research. In addition, these laboratory mentors have all been actively involved in training pediatric fellows in projects relevant to Pediatric Infectious Diseases. The training program consists of: 1) a formalized research project in the area of basic microbiology, immunology, molecular biology, or virology under the direction of one of the laboratory mentors 2) an organized series of graduate level courses, lectures, seminars, journal clubs, and other conferences;3) regular presentation of research in progress for constructive criticism;and 4) involvement in ongoing clinical activities within the Division of Pediatric Infectious Diseases (qualifying the fellow to sit for Board certification in Pediatric Infectious Diseases). The Department of Pediatrics will support successful fellows wishing additional years of research training. This training program has as its goal producing well-trained physician-scientists who are capable of developing their own independent research programs in areas relevant to infections in the immunocompromised host.